In various contexts, it is useful to be able to predict the fertility of a male mammal. Thus, animal breeders are concerned to use males likely produce offspring of desirable genetic traits. However, it is also important to such animal breeders that fertilization actually take place as a consequence of any given attempt to artificially inseminate a female. For example, in the bovine artificial insemination industry, bulls are evaluated on the basis of the milk production and other characteristics of their daughters. However, a bull of low fertility, as measured by the number of times a cow must be artificially inseminated before pregnancy occurs, is of reduced value. In extreme cases, such bulls are disposed of.
Currently, in the bovine artificial insemination industry, bulls are evaluated for fertility by a process that takes from five to six years to complete. When a breeder examines a one-year-old, sexually mature bull, the breeder's only source of information about the bull's fertility is the pedigree information available on the animal. Testicular size and other gross physical characteristics of the animal provide little or no useful information relating to fertility. Typically such a bull first is bred to cows until as many as 200 daughters are produced and monitored for milk production. It takes as much as four years to do this, because the daughters themselves must become sexually mature so that they can be impregnated, calve, and begin to produce milk. If daughter milk production is good, the bull is kept and included in the breeder's general breeding program. Only at that time is the bull bred to a population of cows sufficiently large for the breeder to judge its fertility.
If a bull's fertility is found to be unacceptably low, the bull is disposed of. Typically, only one out of seven bulls are kept after evaluation of the bull's progeny and fertility has been completed. In the meantime, the breeder has spent a large amount of money and time to maintain and breed the bulls that have been eliminated. If at least some of the bulls destined to be eliminated could be detected as being of low fertility early in the evaluation process, considerable money could be saved.
In other contexts, it is also useful to evaluate quickly the fertility of a breeding male. Breeding males for various types of animals are sold for use in a farmer's herd or for addition to the stud string of an artificial inseminator. Presently there is no widely used method of evaluating fertility of an animal so sold unless statistical data has been amassed on the animal's past production. The purchase of such animals tends to be blind speculation, at least with regard to fertility. The availability of a method for evaluating fertility in a short period of time could thus be of value both to the seller who desires to substantiate the reasonableness of a high price for his animal and to the buyer who wants to know in advance what he is getting.
It would be advantageous in other contexts to be able to test male fertility without having to monitor actual impregnations. Thus, medical personnel concerned with human fertility can evaluate the sperm count of a male but have no generally used, effective conventional means of evaluating the capability of that sperm to fertilize an ovum in vivo. Similarly, it would be desirable to be able to evaluate the fertility of male zoo animals and other animals in which fertility cannot be determined conveniently, economically, or in a socially practical way by attempted fertilization of large numbers of females.
Before mammalian spermatozoa are capable of fertilizing ova, they must undergo capacitation and the acrosome reaction. In vivo, capacitation occurs when mammalian spermatozoa reside for a time in the female reproductive tract. See J. M. Bedford (1970), "Sperm Capacitation and Fertilization in Mammals." Biol. Reprod., Supp. 2, 128-158. Capacitation seems to require the removal of components from the spermatozoa that are epididymal or seminal plasmatic in origin. See S. Aonuma, et al. (1973), "Studies on Sperm Capacitation: I. The Relationship Between a Guinea Pig Sperm Coating Antigen and a Sperm Capacitation Phenomenon." Reprod. Fertil., 35 425-432. After capacitation has occurred, the sperm are able to undergo the acrosome reaction. The acrosome reaction releases enzymes that digest the matrix of the cumulus cells surrounding the ovum. This digestion of the matrix permits the zona pellucida to be penetrated by spermatozoa, so that the sperm may make their way toward the ovum. See D. W. Fawcett (1975), "The Mammalian Spermatozoon." Dev. Bio., 44, 394-436; and R. Yanagimachi (1978), "Sperm-Egg Association in Mammals." Curr. Top. Dev. Biol., 12, 83-105.
It is believed that gycosaminoglycans (hereinafter GAGs) enhance capacitation or at least enhance the incidence of acrosome reactions in mammals. See C. N. Lee, R. W. Lenz, and R. L. Ax (1983), "Bovine Sperm Undergo Capacitation When Exposed to Glycosaminoglycans In Vitro." 75th Ann. Mtng. Soc. Anim. Sci. Abstract 530; and R. W. Lenz, M. E. Bellin, and R. L. Ax (1983), "Rabbit Spermatozoa Undergo and Acrosome Reaction in the Presence of Glycosaminoglycans." Gamete Res., 8, 11. GAGs are found in follicular fluid (H. G. Grimek and R. L. Ax [1982], "Chromatographic Comparison of Chondroitin-Containing Proteoglycan from Small and Large Bovine Ovarian Follicles." Biochem. Biophys. Res. and Comm., 104, 1401.), and in all regions of the bovine female reproductive tract (C. N. Lee and R. L. Ax [1984], "Concentrations of Glycosaminoglycans in the Female Bovine Reproductive Tract." J. Dairy Sci., G7, 2006-2009. Consequently, it is likely that they play an important role in vivo to capacitate sperm. Nevertheless, it is not known precisely what components of the female reproductive tract enhance the ability of sperm to undergo capacitation and the acrosome reaction. R. L. Ax, K. Dickson, and R. W. Lenz (1985), "Induction of the Acrosome Reaction in Response to Chondroitin Sulfates In Vitro Is Related to Non-return Rates of Dary Bulls." J. Dairy Sci., 68, 387-390, have reported that nonreturn rates for bulls used in the artificial insemination industry corresponded to the effectiveness with which acrosome reactions could be induced in vitro by a GAG.
It is knwon that certain GAGs specifically bind to mammalian sperm. Thus, specific binding of the radioactively tagged GAG .sup.3 H-heparin has been reported for human, bovine, rabbit, and monkey sperm. See N. N. Delgado, et al. (1982), "Heparin Binding Sites in the Human Spermatozoa Membrane." Arch. Androl., 8, 87; and R. R. Handrow, et. al. (1984), "Specific Binding of the Glycosaminoglycan .sup.3 H-Heparin to Bull, Monkey, and Rabbit Spermatozoa In Vitro." J. Androl, 5, 51. The binding interaction observed was typical of a receptor-ligand interaction such that dissociation constants could be determined, together with a determination of the number of heparin binding sites on the sperm.